Scientists of the PRISMA+ Cluster of Excellence examine information from the gravitational wave observatory NANOGrav.
The NANOGrav Collaboration just recently recorded the very first indications of really low-frequency gravitational waves. Prof. Pedro Schwaller and Wolfram Ratzinger examined the information and, in specific, thought about the possibility of whether this might point towards brand-new physics beyond the Standard Model. In a short article released in the journal SciPost Physics, they report that the signal follows both a stage shift in the early universe and the existence of a field of very light axion-like particles (ALPs). The latter are thought about as appealing prospects for dark matter.
Gravitational waves open a window into the early universe. While the common cosmic microwave background yields no ideas about the very first 300,000 years of our universe, they offer some peeks of what took place throughout Big Bang. “It’s exactly this very early universe that is so exciting for particle physicists,” describes Pedro Schwaller, Professor of Theoretical Physics at the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz (JGU). “This is the time when the elementary particles like quarks and gluons are present, and then combine to form the building blocks of atomic nuclei.”
The unique aspect of the gravitational waves which the NANOGrav Collaboration has actually identified for the very first time is that they have an extremely low frequency of 10-8 Hertz, which relates to around one oscillation each year. Due to their likewise big wavelength, in order to discover them any detector would likewise need to be similarly big. As such a detector is not possible here on Earth, the astronomers at NANOGrav utilize far-off pulsars and their light signals as substantial detectors.
Wolfram Ratzinger details the inspiration behind their work: “Even though so far the data only provides us with a first hint of the existence of low-frequency gravitational waves, it is still very exciting for us to work with them. This is because such waves could be produced by various processes that occurred in the early universe. We can now use the data we already have to decide, which of these come into consideration and which do not fit the data at all.”
As an outcome, the Mainz-based researchers chose to take an especially close take a look at 2 circumstances that might have triggered the observed gravitational waves: Phase shifts in the early universe and a dark matter field of very light axion-like particles (ALPs). Phase shifts such as these take place due to the falling temperature level in the primitive soup after the Big Bang and lead to enormous turbulences – nevertheless, like dark matter they are not covered by the Standard Model.
Based on the information offered, Pedro Schwaller and Wolfram Ratzinger analyze the outcomes of their analysis with relative care: “Perhaps slightly more probable is the early phase transition scenario.” On the other hand, the 2 physicists think that the reality that they have the ability to exercise specific possibilities based just on restricted information shows the capacity of their method. “Our work is a first, but important development – it gives us a lot of confidence that with more precise data we can draw reliable conclusions about the message gravitational waves are sending us from the early universe.”
“Furthermore,” Pedro Schwaller concludes, “we can already begin to pin down certain characteristics of the scenarios and put constraints on them, in our case the strength of the phase transition and the mass of the axions.”
Reference: “Whispers from the dark side: Confronting light new physics with NANOGrav data” by Wolfram Ratzinger and Pedro Schwaller, 23 February 2021, SciPost Physics.
DOI: 10.21468/SciPostPhys.10.2.047
